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Astron. Astrophys. 363, 198-207 (2000)


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Spectral analysis of multi mode pulsating sdB stars *

II. Feige 48, KPD 2109+4401 and PG 1219+534

U. Heber 1, I.N. Reid 2 and K. Werner 3

1 Dr.-Remeis-Sternwarte, Universität Erlangen-Nürnberg, Sternwartstrasse 7, 96049 Bamberg, Germany (heber@sternwarte.uni-erlangen.de)
2 Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104-6396, USA (inr@herschel.physics.upenn.edu)
3 Institut für Astronomie und Astrophysik, Universität Tübingen, 72076 Tübingen, Germany (werner@astro.uni-tuebingen.de)

Received 2 August 2000 / Accepted 25 August 2000

Abstract

Three members of the new class of pulsating sdB stars (sdBV or EC 14026 stars) are analysed from Keck HIRES spectra using line blanketed NLTE and LTE model atmospheres. Atmospheric parameters ([FORMULA], log g, log(He/H)), metal abundances and rotational velocities are determined. A careful investigation of several temperature indicators, i.e. line profile fitting of Balmer and helium lines, the ionization equilibria of helium, nitrogen and silicon gave consistent results for Feige 48 and KPD2109+4401 to within a few hundred Kelvin. However, for PG 1219+534 considerably higher effective temperature estimates were derived from the ionization equilibria of nitrogen (36 800 K) and helium (34 400 K) than from the Balmer line profile fitting (33 200 K). A systematic difference in the gravity derived from NLTE and LTE models was observed, the NLTE gravities being slightly lower, by up to 0.1 dex, than the LTE results.

As is typical for sdB stars, all programme stars are found to be helium deficient, with a helium abundance ranging from 1/80 solar for Feige 48 to 1/3 solar for PG 1219+534, probably due to diffusion. Most metals are also depleted. The abundances of C, O, Ne, Mg, Al and Si in the high gravity programme stars KPD 2109+4401 and PG 1219+534 are considerably lower than in the lower gravity stars Feige 48 and PG 1605+072 (Heber et al. 1999a) which could be explained by an equilibrium between gravitational settling and radiative levitation. Surprisingly iron is solar to within error limits in all programme stars irrespective of their gravity, confirming predictions from diffusion calculations of Charpinet et al. (1997).

The metal lines are very sharp and allow the microturbulent velocity to be constrained to be lower than 5 km s-1 (KPD 2109+4401, PG 1219+534). Also the projected rotational velocities have to be very low (vrot sini [FORMULA] 10 km s-1). For Feige 48 the limits are even tighter (vmicro[FORMULA]3 km s-1, vrot sini [FORMULA] 5 km s-1).

Key words: stars: abundances – stars: atmospheres – stars: general – stars: oscillations – stars: rotation – stars: subdwarfs

* Based on observations obtained at the W.M. Keck Observatory, which is operated by the Californian Association for Research in Astronomy for the California Institute of Technology and the University of California

Send offprint requests to: U. Heber

© European Southern Observatory (ESO) 2000

Online publication: December 5, 2000

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